Generally, in installing a bridge girder on a pier in a bridge building work, a bridge girder block manufactured to an optional size beforehand in a factory is transported up to the building site, then the block is supported temporarily onto a shoring while being suspended with a crane, the block thus temporarily supported is then combined with another like block and thereafter the thus-combined block is installed onto a pier. In this case, after the bridge girder has been installed onto the pier, the shoring is disassembled or removed.
However, assembling and disassembling the shoring in the building site lead to not only deteriorated working efficiency but also deteriorated economy. In view of this point there has recently been developed such a collapsible shoring as is disclosed, for example, in Japanese Utility Model Laid Open No.8416/95. During transport, this collapsible shoring can be folded in a compact shape, while for use in a building site, it is unfolded in a cubic fonn. Thus, it is employable for each building site without the need of assembly and disassembly.
The shoring disclosed in the above unexamined publication comprises a pair of fixed frames opposed to each other, a pair of collapsible reinforcing frames pivotally connected to both right and left ends of the fixed frames, and floor plates whose base ends are pivotally connected rotatably to inside intermediate positions of the fixed frames.
The reinforcing frames each comprise collapsible baluster struts pivotally mounted between the upper ends of struts as constituents of the fixed frames, collapsible horizontal members pivotally mounted between the struts, braces pivotally connected to the upper ends of the struts and to an intermediate position of the horizontal members, and a vertical member mounted between an intermediate position of the baluster struts and an intermediate position of the horizontal members. While in use, the shoring is unfolded in a cubic form, but while not in use, for example during transport, the lower ends of the braces are disengaged from the horizontal member, and the reinforcing frames are folded into a compact shape as a whole when compressed longitudinally by virtue of their own weight.
In the above conventional shoring, however, the reinforcing frames are of a collapsible structure and no reinforcing member is present below the horizontal member, with only two braces being present above. Thus, against vertical and transverse loads, both durability and strength are ensured in the presence of the fixed frames and there is no fear of deformation, but there is weakness against longitudinal loads, for example, against vibrations and it is likely that there may occur deformation in the direction of compression. Further, for folding in a compact shape, it is necessary to take the trouble of disconnecting the lower ends of the braces from the fulcrum of the horizontal member. Thus, the working efficiency is deteriorated markedly.
In view of the above-mentioned point the present inventor has previously developed a shoring having durability against not only vertical and transverse loads but also longitudinal loads and capable of being folded automatically without the need of any extra work.
The said shoring, as disclosed in Japanese Patent Laid Open No.31923/97, comprises a pair of fixed frames opposed to each other, a pair of collapsible reinforcing frames disposed between both ends of the fixed frames, and floor plates whose base ends are pivotally secured to inside intermediate positions of the fixed frames. The reinforcing frames each comprise collapsible baluster struts whose base ends are pivotally secured to the upper ends of the fixed frames, four expansible/retractable braces whose base ends are pivotally connected to upper and lower ends of the fixed frames which extend obliquely toward an inside middle position, a support member comprising a flange for pivotal connection with the front ends of the braces and a guide cylinder provided on the back of the flange, a support rod whose base end is fixed to an intermediate position of the baluster struts and whose lower end is fixed or inserted slidably and selectively into the guide cylinder, and a bracket mounted at the lower end of the support rod to rotatably connect therewith the front ends of the floor plates.
The above shoring is superior in both strength and function, but is desired to be improved in the following points.
The four braces are each of an expansible/retractable mechanism comprising an outer tube and an inner tube. The front ends of the four braces are gathered and connected to a strong flange. The flange is provided with a guide cylinder, into which the support rod is inserted slidably. Thus, the structure is complicated and this complicated structure results in an increase of both manufacturing cost and weight. Therefore, when the shoring is folded or when it is restored to its cubic state from the folded state, the associated work is difficult and so is the work for transport.